It has long been assumed that dinosaurs, like today's reptiles, were cold-blooded. In other words, a dinosaur's body temperature was thought to equal that of its environment. Recently, however, a number of scientists have put forward a suggestion that dinosaurs were, in fact, warm-blooded animals that maintained a constant body temperature, and they support this new theory with several arguments.
First, the ability of dinosaurs to dominate the warm-blooded mammals during the millions of years the two groups coexisted on Earth suggests that dinosaurs enjoyed the physiological advantages of being warm-blooded. For example, warm-blooded animals tolerate cold temperatures much better and use energy from food much more efficiently than cold-blooded animals. Had the dinosaurs been cold-blooded, it is hard to imagine how they could successfully compete with the mammals, much less dominate them.
Second, since warm-blooded animals have more surplus energy than cold-blooded ones, they typically care for their young much more extensively. Fossil remains of dinosaur nests provide evidence of highly developed parental care. The nests contain remains of very young dinosaurs, indicating that young dinosaurs grew up in the nest and were fed by their parents. Furthermore, the nests contain very small fragments of dinosaur eggshells, which suggest that the young stayed in the nest long enough to break the eggshells into small pieces as they trampled on them. All this evidence points to the conclusion that the young dinosaurs received a lot of parental care, which is a typical feature of warm-blooded animals.
Third, fossil evidence suggests that dinosaurs may have regulated body temperature by developing hair- and feather-like outer structures similar to those used by birds and mammals. No cold-blooded animal today has such coverings. Since many dinosaurs appear to have grown hair and feathers, dinosaurs must have been warm-blooded like the animals that grow them today.
Summarize the points made in the lecture, being sure to explain how they challenge the specific claims made in the reading passage.
In the lecture, the professor casts doubt on the reading passage’s idea that dinosaurs were warm-blooded animals. The professor asserts that the evidence supporting the warm-blooded theory is questionable and can be easily refuted.
Firstly, the passage claims that dinosaurs' dominance over mammals suggests they had the physiological advantages of being warm-blooded. By contrast, the professor asserts that cold-blooded animals can also dominate ecosystems. He gives the example of the Komodo dragon, a cold-blooded reptile that is a top predator capable of hunting large mammals, demonstrating that dinosaurs could have been dominant even if they were cold-blooded.
Secondly, the author of the passage points out that evidence of dinosaur nests and young dinosaurs implies extensive parental care typical of warm-blooded animals. However, the lecture notes that an analysis of young dinosaurs' leg bones shows they were mobile and likely able to find food on their own, meaning that the nests do not necessarily indicate parental feeding behavior, thus weakening the argument for warm-bloodedness.
Lastly, the reading states that dinosaurs developed hair- and feather-like structures, similar to modern warm-blooded animals. On the contrary, the professor contends that these structures may not have served as insulation. Instead, he suggests that dinosaurs could have used them for other purposes, such as attracting mates or providing camouflage, so the presence of hair or feathers does not prove dinosaurs were warm-blooded.
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